Device for screening convergence insufficiency and related computer implemented methods

ABSTRACT

A device is for screening a person for CI and may include a binocular viewer, a display adjacent the binocular viewer, and a processor and associated memory cooperating with the display. The processor may be configured to display on the display a first visual stimulus and a second visual stimulus, cause, in alternating fashion, convergent movement and divergent movement in the first visual stimulus and the second visual stimulus along a visual stimulus path, determine respective centroid positions of the second eye and the first eye during the convergent and divergent movement of the first visual stimulus and the second visual stimulus, and calculate an IPD, and compare the IPD with the visual stimulus path to obtain a dynamic IPD, the dynamic IPD serving as an indicator for whether the person has CI.

RELATED APPLICATION

This application is based upon prior filed Application No. 62/385,136filed Sep. 8, 2016, the entire subject matter of which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

This present application relates to a medical device, and moreparticularly, to a device for screening visual issues in a patient.

BACKGROUND

Convergence Insufficiency (CI) occurs when a subject's brain fails tocoordinate images from both eyes while trying to focus on a nearbyobject. When a subject reads or looks at a close object, the subject'seyes must both turn inwardly (convergence) to focus. In studies thatused standardized definitions of Convergence Insufficiency,investigators have reported a prevalence of 4.2% to 6% in school andclinic settings. Convergence Insufficiency is a common binocular visiondisorder that is often associated with a variety of symptoms, includingeyestrain, headaches, blurred vision, diplopia (double vision),sleepiness, difficulty concentrating, movement of print while reading,and loss of comprehension after short periods of reading or performingclose activities.

Also, CI can cause difficulty with reading. This may make parents orteachers suspect that a child has a learning disability, instead of aneye disorder. In the past, CI disorder has often gone undetected becauseCI testing is not included in (1) a pediatrician's eye test; (2) schoolscreenings; or (3) basic eye exams. A person can pass the 20/20 eyechart test and still have CI.

Currently, there is no consensus on norms for existing clinical methodsfor detecting CI or whether these are the only clinical measuresrequired. Multiple subjective and objective decisions, includingestimates of distance and time, are required by both the subject and theclinician. Objective measurements rely on examiner expertise and may bedifficult for beginners to observe. Subjective measurements requirepatient cooperation to attain reliable results. In summary, presentclinical methods have significant problems regarding accuracy andreproducibility, because they require subjective feedback from thesubject, and because of clinician variability.

SUMMARY

Generally, a device is for screening a person for CI. The device mayinclude a binocular viewer comprising a first eyepiece to receive afirst eye of the person, a second eyepiece to receive a second eye ofthe person, a first image sensor adjacent the first eyepiece, and asecond image sensor adjacent the second eyepiece, a display adjacent thebinocular viewer, and a processor and associated memory cooperating withthe display. The processor may be configured to record, with the firstimage sensor, movement of the first eye, record, with the second imagesensor, movement of the second eye, and display on the display a firstvisual stimulus and a second visual stimulus. The processor may beconfigured to cause, in alternating fashion, convergent movement anddivergent movement in the first visual stimulus and the second visualstimulus along a visual stimulus path, determine respective centroidpositions of the second eye and the first eye during the convergent anddivergent movement of the first visual stimulus and the second visualstimulus, and calculate an interpupillary distance (IPD), and comparethe IPD with the visual stimulus path to obtain a dynamic IPD, thedynamic IPD serving as an indicator for whether the person has CI.

In some embodiments, a duration of each of the convergent movement andthe divergent movement is 80-100 seconds. The device may also include afirst infrared (IR) source configured to irradiate the first eye and asecond IR illuminator configured to irradiate second eye, and theprocessor and memory may be configured to generate a first plurality ofvideo frames showing movement of the first eye, and generate a secondplurality of video frames showing movement of the second eye.

More specifically, the processor and memory may be configured toidentify second blink pixels comprising second eye blinks in the secondplurality of video frames, and form a third plurality of video frames byremoving the second blink pixels from the second plurality of videoframes. The processor and memory may be configured to identify firstblink pixels comprising first eye blinks in the first plurality of videoframes, and form a fourth plurality of video frames by removing thefirst blink pixels from the first plurality of video frames.

Also, the processor and memory may be configured to generate the firstplurality of video frames by performing at least filtering each of thefirst plurality of video frames using a pixel intensity threshold toform a third plurality of video frames, each of the third plurality ofvideo frames comprising a black background in combination with a whitebackground, a first eye image, the third plurality of video framescomprising an N number of video frames, and filtering each of the secondplurality of video frames using the pixel intensity threshold to form afourth plurality of video frames, each of the fourth plurality of videoframes comprising a black background in combination with a whitebackground, a second eye image, the fourth plurality of video framescomprising an M number of video frames. The processor and memory may beconfigured to generate the first plurality of video frames by performingat least determining, for each of the third plurality of video frames, xand y coordinates for a first eye pupil centroid, and generating a firstplurality of x coordinate datasets. An ith x coordinate datasetrepresents a location of an ith second pupil centroid, and i is greaterthan or equal to 1 and less than or equal to N. The processor and memorymay be configured to generate the first plurality of video frames byperforming at least determining, for each of the fourth plurality ofvideo frames, x and y coordinates for a second eye pupil centroid, andgenerating a second plurality of x coordinate datasets. A jth xcoordinate dataset represents a location of a jth first pupilarcentroid, and j is greater than or equal to 1 and less than or equal toM.

The processor and memory may be configured to graphically display afirst curve comprising N x coordinate datasets versus time, andgraphically display a second curve comprising M x coordinate datasetsversus time. The processor and memory may also be configured to set i=1and j=1, subtract the ith x coordinate dataset from the jth x coordinatedataset to form a kth x coordinate dataset, each of the kth x coordinatedataset representing a hth dynamic IPD, when i is less than N, seti=i+1, when j is less than M, set j=j+1, and repeat the setting and thesubtracting until at least one of i=N and j=M is true.

The processor and memory may be configured to form a third curvecomprising each of the hth dynamic IPD versus time. The processor andmemory may be configured to identify a first substantially linearportion of the third curve, the first substantially linear portioncomprising a positive slope, identify a second substantially linearportion of the third curve, the second substantially linear portioncomprising a negative slope, generate a graphical plot of the visualstimulus path, the graphical plot comprising a first linear portioncomprising a positive slope and a second linear portion comprising anegative slope, overlap the third curve onto the graphical plot of thevisual stimulus path, and adjust the third curve to fit onto graphicalplot of the visual stimulus path. The processor and memory may beconfigured to compare the dynamic IPD with the visual stimulus path byperforming at least optimizing a graph of dynamic IPDs with at least oneparameter, and merging the optimized graph of dynamic IPDs with thevisual stimulus path.

Another aspect is directed to a method for screening a person for CI.The method may include recording, with a first image sensor, movement ofa first eye of the person, recording, with a second image sensor,movement of a second eye of the person, and displaying on a display afirst visual stimulus and a second visual stimulus. The method mayinclude causing, in alternating fashion, convergent movement anddivergent movement in the first visual stimulus and the second visualstimulus along a visual stimulus path, determining respective centroidpositions of the second eye and the first eye during the convergent anddivergent movement of the first visual stimulus and the second visualstimulus, and using a processor and memory associated with the display,and the first and second image sensors for calculating an interpupillarydistance (IPD), and comparing the IPD with the visual stimulus path toobtain a dynamic IPD, the dynamic IPD serving as an indicator forwhether the person has CI.

Another aspect is directed to a device for screening a person for CIwith a binocular viewer comprising a first eyepiece to receive a firsteye of the person, a second eyepiece to receive a second eye of theperson, a first image sensor adjacent the first eyepiece, and a secondimage sensor adjacent the second eyepiece. The device may include adisplay adjacent the binocular viewer, and a processor and associatedmemory cooperating with the display. The processor may be configured torecord, with the first image sensor, movement of the first eye, record,with the second image sensor, movement of the second eye, and display onthe display a first visual stimulus and a second visual stimulus. Theprocessor may be configured to cause, in alternating fashion, convergentmovement and divergent movement in the first visual stimulus and thesecond visual stimulus along a visual stimulus path, determinerespective centroid positions of the second eye and the first eye duringthe convergent and divergent movement of the first visual stimulus andthe second visual stimulus, and calculate an interpupillary distance(IPD), and compare the IPD with the visual stimulus path to obtain adynamic IPD, the dynamic IPD serving as an indicator for whether theperson has CI.

Another aspect is directed to a non-transitory computer-readable mediumhaving computer-executable instructions for causing a computing devicecomprising a processor and associated memory to perform a method forscreening a person for CI. The method may include recording, with afirst image sensor, movement of a first eye of the person, recording,with a second image sensor, movement of a second eye of the person, anddisplaying on a display a first visual stimulus and a second visualstimulus. The method may include causing, in alternating fashion,convergent movement and divergent movement in the first visual stimulusand the second visual stimulus along a visual stimulus path, determiningrespective centroid positions of the second eye and the first eye duringthe convergent and divergent movement of the first visual stimulus andthe second visual stimulus, and calculating an IPD, and comparing theIPD with the visual stimulus path to obtain a dynamic IPD, the dynamicIPD serving as an indicator for whether the person has CI.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an apparatus to screen for CI,according to the present disclosure.

FIG. 2A is a schematic diagram of a binocular viewer 110 and a housingcomprising one visual display, according to the present disclosure.

FIG. 2B is a schematic diagram of binocular viewer and the housingcomprising one movable visual display, according to the presentdisclosure.

FIG. 3A is a schematic diagram of another embodiment of the binocularviewer and the housing comprising two visual displays, according to thepresent disclosure.

FIG. 3B is a schematic diagram of another embodiment of the binocularviewer and the housing comprising two movable visual displays, accordingto the present disclosure.

FIG. 4 is a flowchart showing a method to objectively screen for CI,according to the present disclosure.

FIG. 5 is a flowchart showing a method to process and analyze eyemovement data recorded by cameras, according to the present disclosure.

FIG. 6A is a graph illustrating a programmed visual stimulus path,according to the present disclosure.

FIGS. 6B-6D are schematic diagrams showing the visual stimuli movingconvergently and divergently, according to the present disclosure.

FIG. 7 are analog video frames of recorded eye movement at a certaintime point, according to the present disclosure.

FIG. 8 are analog video frames of recorded eye movement during a blink,according to the present disclosure.

FIGS. 9A-9D are eye movement images, according to the presentdisclosure.

FIG. 10 is a graph of pupil positions in pixel numbers versus time andIPDs in pixel numbers versus time, according to the present disclosure.

FIG. 11 is a graph of IPDs in millimeters versus time, according to thepresent disclosure.

FIG. 12 is a graph of dynamic IPDs in millimeters versus times with anadjusted y-axis scale, according to the present disclosure.

FIGS. 13A-13C are graphs showing dynamic IPDs in degrees and prismdiopters versus time, according to the present disclosure.

FIG. 14 is a graph of pupil positions in millimeters versus time ofdifferent sets of recorded eye movement during different cycles ofvisual stimuli convergence and divergence displaying, according to thepresent disclosure.

FIG. 15 is a schematic diagram of a controller depicted in FIG. 1.

FIGS. 16A and 16B are graphs of testing results in prism diopters,according to the present disclosure.

FIGS. 17-18 are images of example embodiments of the binocular viewerand associated equipment.

FIG. 19 is an image of an example embodiment for testing the device,according to the present disclosure.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which several embodiments ofthe invention are shown. This present disclosure may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the present disclosure to those skilled in theart. Like numbers refer to like elements throughout.

Certain embodiments of Applicant's disclosure recite a method to screena person for CI. The steps of the method comprise providing a screeningapparatus, positioning a patient in front of the screening apparatus sothat the patient looks into the apparatus, displaying visual stimuliconvergently and divergently to generate a visual stimulus path,determining respective centroid positions of each eye, calculating aninterpupillary distance (IPD) between the eyes, and comparing the IPDwith the visual stimulus path to obtain a dynamic IPD, which is anindicator for whether the patient has CI.

Further, certain embodiments of Applicant's disclosure describe thescreening apparatus with a binocular viewer and a housing attached tothe binocular viewer. Further, the binocular viewer comprises twoeyepieces, two mirrors, and two infrared (IR) illuminators; and thehousing comprises two video cameras and a visual display device. Incertain embodiments, the visual display is movable.

In certain embodiments, the binocular viewer comprises two eyepieces andtwo mirrors. The binocular viewer does not contain any (IR)illuminators. In other embodiments, the binocular viewer comprises twoeyepieces, four mirrors, and two infrared (IR) illuminators. In yet someother embodiments, the binocular viewer comprises two eyepieces and fourmirrors, without the IR illuminators. In addition, in certainembodiments, the visual display is movable.

The Applicant's disclosure is described in preferred embodiments in thefollowing description with reference to the Figures, in which likenumbers represent the same or similar elements. Reference throughoutthis specification to “one embodiment,” “an embodiment,” or similarlanguage means that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment.

The described features, structures, or characteristics of the inventionmay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are recited toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventionmay be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

As a general matter when viewing an object, humans and many otheranimals enjoy stereoscopic vision. Because the two eyes are separatedhorizontally, the images perceived in the two eyes are slightlydifferent and the difference is proportional to the relative depth. Thevisual areas in the brain measure these differences, and “merge” the twodifferent objects into a single object. In overview, Applicant'sapparatus and method provide a mechanism to evaluate the ability of thesubject's brain to merge the two perceived objects into a single 2-D or3-D image.

Referring now to FIG. 1, Applicant's assembly for objectively screeningsubjects for Convergence Insufficiency comprises a binocular viewer 110,a housing 120 attached to binocular viewer 110, and a controller 130. Asubject 102 is positioned in front of binocular viewer 110. Referringnow to FIGS. 1, 2A and 2B, the subject 102 positions his or her eyes202A and 2028 in front of eyepieces 126 and 128, respectively. Incertain embodiments, the subject 102 places both hands on a surfacesupporting housing 120 to eliminate head movement during theexamination. Further, the distance between the two eyepieces 126 and 128can be adjusted to match a distance between the test subject's eyes 202Aand 202B.

In other embodiments, a virtual reality (VR) mask/headset fits overbinocular viewer 110. Applicant has found that the VR mask faceplate canposition the test subject's head into the best position for testing andreduce movement.

In certain embodiments, Applicant's apparatus comprises two (2) frontsurface mirrors and two (2) cold mirrors disposed in housing 120 and asingle visual display device. In other embodiments, Applicant'sapparatus comprises two (2) front surface mirrors and two (2) coldmirrors disposed in housing 120 and a single visual display device,wherein the visual display device is moveable within the housing.

In yet other embodiments, Applicant's apparatus comprises two (2) frontsurface mirrors and two (2) cold mirrors disposed in housing 120, asingle visual display device, and two (2) infrared emitters disposed inhousing 120. In still other embodiments, Applicant's apparatus comprisestwo (2) different front surface mirrors and two (2) cold mirrorsdisposed in housing 120, a single visual display device, and two (2)infrared emitters disposed in housing 120, wherein the visual displaydevice is moveable within the housing.

In further embodiments, Applicant's apparatus comprises two (2) coldmirrors disposed in housing 120 and two different visual displaydevices. In other embodiments, Applicant's apparatus comprises two (2)front surface (or cold) different mirrors disposed in housing 120 andtwo different visual display devices, wherein one or more of the visualdisplay devices is moveable within the housing. In further embodiments,Applicant's apparatus comprises two (2) different front surface (orcold) mirrors disposed in housing 120, two (2) different visual displaydevices disposed in housing 120, and two (2) infrared emitters disposedin housing 120. In other embodiments, Applicant's apparatus comprisestwo (2) different front surface (or cold) mirrors disposed in housing120, two (2) different visual display devices disposed in housing 120,and two (2) infrared emitters disposed in housing 120, wherein one ormore of the visual display devices is moveable within housing 120.

Referring now to FIGS. 1 and 2A, housing 120 comprises a camera 240, acamera 250, and a visual display 230 (FIG. 2). A controller 130 is incommunication with both cameras 240 and 250, and the visual display 230.Referring now to FIG. 15, controller 1500 comprises processor 1510,memory 1520 interconnected with processor 1510 via communication link1525, optional Bluetooth module 1530 interconnected with processor 1510via communication link 1535, optional RFID module 1540 interconnectedwith processor 1510 via communication link 1545, and optional “WI-FI”module 1550 interconnected with processor 1510 via communication link1555.

In the illustrated embodiment of FIG. 15, microcode 1522, instructions1524, and database 1526, are encoded in memory 1520. In certainembodiments, memory 1520 comprises non-volatile memory. In certainembodiments, memory 1520 comprises battery backed up RAM, a magnetichard disk assembly, an optical disk assembly, and/or electronic memory.By “electronic memory,” Applicants mean a PROM, EPROM, EEPROM,SMARTMEDIA, FLASHMEDIA, and the like.

Processor 1510 uses microcode 1522 to operate controller 1500. Processor1510 uses microcode 1522, instructions 1524, and database 1526, tooperate Applicant's assembly 100, Bluetooth module 1530, RFID module1540, and WI-FI module 1550.

In certain embodiments, processor 1510, memory 1520, optional Bluetoothmodule 1530, optional RFID module 1540, and optional “WI-FI” module1550, are integrated into an application specific integrated circuit,i.e. an “ASIC.”

In the illustrated embodiment of FIG. 2A, the binocular viewer 110comprises two eyepieces 126 and 128, two infrared (IR) emitters 260 and270, and four mirrors 121, 123, 125, and 127. The eyepieces 126 and 128are disposed in surface 110 a of binocular viewer 110. Each eye sees adifferent, moveable stimulus on display 230. In certain embodiments, thestimulus can be white shown on black background. In other embodiments,the stimulus can be black shown on white background.

In certain embodiments, mirrors 123 and 125 are cold mirrors, whichallow light to go through on one side but is reflective on the otherside, such as sides 123 a and 125 a are reflective (FIG. 2A, these sidesfacing subject's eyes); whereas mirrors 121 and 127 are surface mirrors,which reflect normally on one side and the other side is non-reflectiveto avoid extra light issue. For example, sides 121 a and 127 a (FIG. 2a) of the surface mirrors reflect normally. Further, the reflective sideof a cold mirror can block about 90% of visible light, which has aspectrum up to about 650 nanometers. As described herein, “about” isused to describe a plus or minus 10% difference in any measurements. Thenon-reflective sides 123 b and 125 b (FIG. 2A) of mirrors 123 and 125allow cameras 240 and 250 to be positioned behind mirrors withoutcausing obstruction or distraction to testing subjects because they arelooking at the reflective sides 123 a and 125 a of the mirrors duringthe test and cannot see the cameras. Further, in some embodiments, an IRfilter 150 (FIG. 2B) is disposed parallel to mirror 125 and another IRfilter 152 (FIG. 2B) is disposed parallel to mirror 123. The IR filtersblock light of wavelengths up to about 700 nanometers and they assist inpreventing the light from leaking back into the cameras 240 and 250,which will cause blur or glare.

A first eye 202A of a test subject 102 looks through the eyepiece 126 toobserve moveable visual stimulus 236 shown on visual display 230. Asight path for first eye 202A passes through eyepiece 126 onto mirror123, is redirected by reflective surface 123 a onto mirror 121, isredirected by reflective surface 121 a onto display 230.

A second eye 2028 of a test subject 102 looks through the eyepiece 128to observe moveable visual stimulus 234 shown on visual display 230. Asight path for second eye 202A passes through eyepiece 128 onto mirror125, is redirected by reflective surface 125 a onto mirror 127, isredirected by reflective surface 127 a onto display 230.

Mirror 121 and surface 110 a define a dihedral angle θ_(a). Mirror 127and surface 110 a define a dihedral angle θ_(b). In certain embodiments,angles θ_(a) and θ_(b) are about 135°. In a non-limiting embodiment, thedihedral angle between mirrors 123 and 125 is a right angle, i.e., thedihedral angle is about 90°.

Mirror 123 is substantially parallel to mirror 121, with a reflectiveside 123 a having a facing relationship with the reflective side 121 aof mirror 121. Mirror 125 is substantially parallel to mirror 127 withreflective side 125 a having a facing relationship with reflective side127 a of mirror 127.

Further, in the illustrated embodiment of FIG. 2A, infrared (IR) emitter270 is disposed adjacent eyepiece 126, and between mirrors 121 and 123.Similarly, the infrared emitter 260 is disposed adjacent eyepiece 128,and between the mirrors 125 and 127. As those skilled in the art willappreciate, infrared radiation IR is invisible to human eyes, andcomprises wavelengths longer than those of visible light, extending fromthe nominal red edge of the visible spectrum at 700 nanometers(frequency 430 THz) to 1 mm (300 GHz). In a preferred embodiment, the IRemitters 260 and 270 operate at a wavelength of 940 nanometers, whicheliminates any distraction to a testing subject.

Applicant has found that illuminating the eyes with infrared radiationeliminates unwanted artifacts in an eye image. The most distinctivefeature in a recorded eye image is the contour of the pupil rather thanlimbus. Both the sclera and the iris strongly reflect infrared light,while only the sclera reflects visible light.

Applicant has further found that tracking the sharp contour of the pupilinstead of the iris gives more reproducible results because the smallsize of the pupil makes it less likely to be occluded by an eyelid.Binocular viewer 110 and housing 120 are designed to block visiblelight. Therefore, infrared eye tracking can be employed withoutinterference from visible light.

Referring to the illustrated embodiment of FIG. 2A again, housing 120 isattached to binocular viewer 110, and comprises video camera 240 whichis in communication with controller 130 via communication link 242,video camera 250 which is in communication with controller 130 viacommunication link 252, and visual display 230 which is in communicationwith controller 130 via communication link 232. Video camera 240transmits eye movement data in digital video frame to the controller 130via communication link 242. In certain embodiments, digital video framedata is transferred by video camera 240 to controller 130 in a digitalbit stream. In certain embodiments, digital video frame data istransferred by video camera 240 to controller 130 as a digitized analogsignal.

Video camera 250 transmits eye movement data in digital video frame tothe controller 130 via communication link 252. In certain embodiments,digital video frame data is transferred by video camera 250 tocontroller 130 in a digital bit stream. In certain embodiments, digitalvideo frame data is transferred by video camera 250 to controller 130 asa digitized analog signal. In certain embodiments, the cameras 240 and250 operate on fixed focus lenses, which are adjustable. In otherembodiments, cameras 240 and 250 operate on auto focus lenses. In yetother embodiments, cameras 240 and 250 operate on telocentric lenses. Instill other embodiments, cameras 240 and 250 operate on extendeddepth-of-field lenses.

In the illustrated embodiment of FIG. 2A, mirror 125 is disposed betweenvideo camera 240 and eyepiece 128. Mirror 125 and IR filter 150 are usedto block the infrared radiation from bouncing back and interfering withthe cameras. Infrared emitter 260 shines infrared light onto eye 202B,and video camera 240 is able to record the movement of eye 202B becauseof that infrared illumination.

In the illustrated embodiment of FIG. 2A, mirror 123 is disposed betweenvideo camera 250 and eyepiece 128. Mirror 123 and IR filter 152 are usedto block the infrared radiation from bouncing back and interfering withthe cameras. Infrared emitter 270 shines infrared light onto eye 202A,and video camera 250 is able to record the movement of eye 202A becauseof that infrared illumination.

Referring now to FIG. 6A, in certain embodiments controller 130 causesthe displayed visual stimuli 234 and 236 to move convergently anddivergently in an alternate manner using a preprogrammed visual stimuluspath. In certain embodiments, visual stimuli 234 and 236 are initiallysubstantially merged on the visual display device. Even though visualstimuli 234 and 236 are not actually merged on the display device, thesubject perceives only a single image because the subject's brain hasformed a single image from the two differing right eye image and lefteye image. In other embodiments, visual stimuli 234 and 236 can startunconverged and move slowly into convergence.

The visual stimuli then move divergently, i.e. away from each other, inaccord with curve 610 until a maximum separation is reached at point630. At some point along curve 610, the subject's brain is unable tomaintain a single image, and the subject perceives two different images.

Thereafter, visual stimuli 234 and 236 move convergently in accord withcurve 620. At some point along curve 620, the subject's brain can onceagain form a single perceived image. In certain embodiments, thedivergent movement of the visual stimuli, followed by convergentmovement of those visual stimuli, takes about 90 seconds.

In certain embodiments, the beginning separation between visual stimuli234 and 236 varies from about 120 to about 150 mm, and preferably atabout 140 mm. In certain embodiments, the maximum separation betweenvisual stimuli 234 and 236 at point 630 (FIG. 6A) varies from about 250to about 310 mm, and preferably at about 300 mm.

In addition, the size of the stimuli 234 and 236 can be increased ordecreased from one examination to another examination. Further, thebrightness and the coloration of the stimuli 234 and 236 vary from oneexamination to another examination.

Referring to FIG. 6A, at point 601, i.e. at the beginning of theprocedure, the visual stimuli are separated by about 125 mm for about 5seconds. Immediately thereafter at point 605, the stimuli are instantlybrought closer, i.e. to a separation of about 40 mm. At point 605, thestimuli begin to separate, i.e. diverge, at a speed of about 1 to 3mm/second, with the preferred speed of about 2 mm/second as shown bylinear curve portion 610 having a positive slope.

When visual stimuli 234 and 236 reach a maximum separation at point 630,which is about 230 mm on the visual display, the visual stimuli thenconverge, i.e. move towards each other (FIG. 6C). At point 657, thevisual stimuli are separated by about 40 mm. Immediately thereafter, thestimuli move apart to a separation of about 125 mm for about 20 seconds,and the procedure ends.

In certain embodiments, the divergence/convergence process repeats twoor more times to generate multiple sets of video frames of eye movementto determine the reproducibility of Applicant's apparatus and method.

In certain embodiments, visual display device 230 can be movedbackwardly/forwardly. In certain embodiments, one or more iterations ofApplicant's method summarized hereinabove are performed with visualdisplay device 230 at a first distance from eyepieces 126 and 128. Thevisual display device is then repositioned at a second distance fromeyepieces 126 and 128, and Applicant's procedure is repeated. In certainembodiments, the second distance is less than the first distance. Inother embodiments, the second distance is greater than the firstdistance.

Referring now to FIG. 2B, in certain embodiments visual display device230 can be move forwardly and/or backwardly within housing 120.Apparatus 205 comprises the elements of apparatus 200, and furthercomprises locomotion assembly 280 a attached to a first end of visualdisplay device 230. Locomotion assembly 280 a is interconnected tocontroller 130 by communication link 284. Locomotion tracks 295 a arepositioned such that moveable wheels disposed on locomotion assembly 280a can be disposed on locomotion tracks 295 a.

Apparatus 205 further comprises locomotion assembly 280 b attached to asecond end of visual display device 230. Locomotion assembly 280 b isinterconnected to controller 130 by communication link 282. Locomotiontracks 295 b are positioned such that moveable wheels disposed onlocomotion assembly 280 b can be disposed on locomotion tracks 295 b.

As described hereinabove, in certain embodiments Applicant's apparatuscomprises two mirror and two visual display devices. For example, in theillustrated embodiment of FIG. 3A, apparatus 300 comprises two mirrorsand two visual display devices.

Apparatus 300 comprises a first mirror 323 comprising reflective surface323 a. Mirror 323 is disposed between eyepiece 126 and video camera 250.Sight path 305 a originates at eyepiece 126, and includes reflectivesurface 323 a, and visual display device 324. Display device 320 isinterconnected to controller 130 via communication link 322.

Apparatus 300 further comprises a second mirror 325 comprisingreflective surface 325 a. Mirror 325 is disposed between eyepiece 128and video camera 240. Sight path 305 b originates at eyepiece 128, andincludes reflective surface 325 a, and visual display device 314.Display device 310 is interconnected to controller 130 via communicationlink 312.

Referring now to FIG. 3B, apparatus 305 includes the elements ofapparatus 300 (FIG. 3A) and further includes a first locomotion assembly280 c attached to a first end of visual display device 310. Locomotionassembly 280 c is interconnected to controller 130 by communication link315. Locomotion tracks 318 are positioned such that moveable wheelsdisposed on locomotion assembly 280 c can be disposed on locomotiontracks 318.

Apparatus 305 further comprises locomotion assembly 280 d attached to asecond end of visual display device 310. Locomotion assembly 280 d isinterconnected to controller 130 by communication link 313. Locomotiontracks 316 are positioned such that moveable wheels disposed onlocomotion assembly 280 d can be disposed on locomotion tracks 316.

Similarly, apparatus 305 comprises a third locomotion assembly 280 eattached to a first end of visual display device 320, which isinterconnected to controller 130 via communication link 322. Locomotionassembly 280 e is interconnected to controller 130 by communication link328. Locomotion tracks 319 are positioned such that moveable wheelsdisposed on locomotion assembly 280 e can be disposed on locomotiontracks 319. In addition, a fourth locomotion assembly 280 f attached toa second end of visual display device 320. Locomotion assembly 280 f isinterconnected to controller 130 by communication link. Locomotiontracks 317 are positioned such that moveable wheels disposed onlocomotion assembly 280 f can be disposed on locomotion tracks 317.

FIG. 4 summarizes the steps of Applicant's method using Applicant'sapparatus. In step 410, the method provides an apparatus configured toscreen subjects for convergence insufficiency. In certain embodiments,the method in step 410 provides apparatus 200 (FIG. 2A). In certainembodiments, the method in step 410 provides apparatus 205 (FIG. 2B). Incertain embodiments, the method in step 410 provides apparatus 300 (FIG.3A). In certain embodiments, the method in step 410 provides apparatus305 (FIG. 3B).

In step 420, the method selects a form for a first visual stimulus.Further in step 420, the method selects a form for a second visualstimulus. In certain embodiments, the form selected for the first visualstimulus is identical to the form selected for the second visualstimulus. For example, FIG. 6B shows a first visual stimulus and asecond visual stimulus, wherein the first visual stimulus comprises thesame form as the second visual stimulus. In other embodiments, the formselected for a first visual stimulus differs from the form selected fora second visual stimulus.

In step 430, the method creates a stimulus path. For example, anillustrated stimulus path is depicted in FIG. 6A. Further, the size, thebrightness, the beginning distance, and the moving speed of the twostimuli are determined in step 430.

In step 440, a testing subject 102 positions his or her eyes to lookinto eyepieces 126 and 128 disposed in binocular viewer 110. In step450, the method initiates visual stimulus movement on one or moreattached visual display devices. In addition, the method synchronouslybegins recording eye movement of both eyes.

In certain embodiments, a controller attached comprising a portion ofthe screening apparatus of step 410 performs step 430. In certainembodiments, a controller attached to the screening apparatus wirelesslyreceives an instruction to perform step 430.

In certain embodiments, recorded video frames of the eye movements ofeye 202A and eye 202B are stored in a non-transitory computer readablemedium 1520 (FIG. 15) by a processor 1510 (FIG. 15) disposed incontroller 130. In certain embodiments, computer readable medium 1520comprises a magnetic storage medium, an optical storage medium, or anelectronic storage medium. By electronic storage medium, Applicant meansa PROM, EPROM, EEPROM, Flash PROM, compactflash, smartmedia, and thelike.

In certain embodiments, the data calculation in steps 460, 470, and 480can be performed after the examination. In other embodiments, the datacalculation in steps 460, 470, and 480 can be performed in real timeduring the examination. In yet other embodiments, the data calculationin steps 460, 470, and 480 can be performed in slightly delayed realtime during the examination. In step 460, the method determines aninterpupillary distance (IPD). IPD is the distance between the centersof the pupils of the two eyes. In certain embodiments, step 460 isperformed by controller 1500 using processor 1510, and microcode 1522,and instructions 1524. In certain embodiments, controller 1500wirelessly receives an instruction to perform step 460.

In step 470, the method graphically curve fits a plot of IPD versustime. Now referring to FIG. 11, the method converts the IPDs in pixelnumbers (FIG. 10) to x coordinates in millimeters (mm). A curve 1110 isa display of IPDs in mm versus time in seconds. Further, a substantiallylinear portion 1120 of the curve 1110 comprising a positive slope andanother substantially linear portion 1130 of the curve 1110 comprising anegative slope are identified. Additionally, random sample consensus(RANSAC), an iterative method to estimate parameters of a mathematicalmodel from a set of observed data which contains errors and/or outliers,is used to remove errors and/or outliers and optimize the curve 1110.

Further in step 470 and referring to FIG. 12, an optimal curve 1210 ofdynamic IPDs is generated by further adjusting the scale of the y-axisin mm. The optimal curve 1210 is overlapped with the visual stimuluspath 640. Further, a substantially linear portion 1220 comprising apositive slope of the curve 1210 overlays with the positive slope 610 ofthe visual stimulus path 640 and another substantially linear portion1230 comprising a negative slope of the curve 1210 overlays with thenegative slope 620 of the visual stimulus path 640. Moreover, point1240, which is the lowest value of a dynamic IPD on curve 1210, is thepoint at which the stimuli appear to have merged for the testing subjectand the point at which the testing subject's convergence should be atits maximum capacity. For example, when the substantially linear portion1230 is long and the valley 1240 reaches down lower towards the x-axis,the testing subject is able to maintain convergence of the stimuli for along time during the moving stimuli test, therefore, the testing subjectis not convergence insufficient. Referring to FIG. 16B, a testingsubject has a dynamic IPD of about −35 prism diopters and displays agood convergence. A range of −20 to −40 prism diopters in dynamic IPD isconsidered a range displaying good convergence. However, when thesubstantially linear portion 1230 is short and the valley 1240 does notreach down far towards the x-axis, the testing subject is not able tomaintain convergence of the stimuli for a long time during the test,therefore, the testing subject may have CI. Referring to FIG. 16A, adifferent testing subject has a dynamic IPD of −15 prism diopters anddisplays a poor convergence.

Referring to FIGS. 13A-13C, the curve 1210 with dynamic IPDs in mm istransitioned to a curve 1310 with dynamic IPDs in degrees. Further, thecurve 1310 with dynamic IPDs in degrees is transitioned to a curve 1320with dynamic IPDs in prism diopters. An antapex 1330 indicates thetesting subject's maximum amount of convergence in prism diopters to thestimuli and is used as the primary determinant for CI.

In certain embodiments, step 470 is performed by controller 1500 usingprocessor 1510, and microcode 1522, and instructions 1524. In certainembodiments, controller 1500 wirelessly receives an instruction toperform step 470.

In step 480, the method determines a dynamic IPD for the test subject.In certain embodiments, step 480 is performed by controller 1500 usingprocessor 1510, and microcode 1522, and instructions 1524. In certainembodiments, controller 1500 wirelessly receives an instruction toperform step 480.

In certain embodiments, step 460 comprises the steps recited in FIG. 5.

Referring to the illustrated embodiment in FIG. 5, step 510, videocamera 250 records the movements of eye 202B and generates a pluralityof video frames during the visual stimuli path described in step 430(FIG. 4) Video camera 240 records the movements of eye 202A andgenerates a plurality of video frames during the visual stimuli pathdescribed in step 430 (FIG. 4). In certain embodiments, the frequency ofthe recorded video frames is about 0.1 sec per frame. A video frame at acertain time point is illustrated in FIG. 7. Referring now to FIG. 8, aneye blink is detected, and the video frame of the blink is furtherremoved from the plurality of video frames generated in step 510 andstep 515. Some testing subjects blink more frequently and use blinkingas a way to reset the convergence system in their eyes. Applicant'sapparatus is able to record the frequency and specific times of occurredblinks, which are additional information that can be utilized todetermine CI.

Referring to FIGS. 9A-9D, the illustrated embodiment of the eye imagesdemonstrates a test analysis sequence. In step 530 and 535, analogpicture frames (FIG. 9A) are directly provided by camera 240 and 250,respectively. In steps 530 and 535, the method sets a pixel intensitythreshold. A pixel intensity threshold is set by a computer readableprogram. In certain embodiments, the computer readable program isMATLAB. In certain embodiments, steps 530 and 535 are performed bycontroller 1500 using processor 1510, and microcode 1522, andinstructions 1524. In certain embodiments, controller 1500 wirelesslyreceives an instruction to perform steps 530 and 535.

In steps 540 and 545, the method applies the pixel intensity thresholdof steps 530 and 535, respectively, to each analog video frame to form abinary eye image illustrated in FIG. 9B comprising a black backgroundand a white 202A or 202B eye image. Further, as illustrated in FIG. 9C,the borders of the binary eye image and small blobs (small white spotsembedded in the black background) are cleared to form a uniform blackbackground, as illustrated in FIG. 9D. Further, referring to FIG. 9D,the x-axis and the y-axis coordinates in pixel numbers of the white eyeblob are determined by the computer readable program. This illustratedtest analysis is repeated with every analog video frame until the lastframe of either eye 202A or 202B to generate a plurality of N videoframes of eye 202A and a plurality of M video frames of eye 202B.

In steps 550 and 555, the method generates a plurality of x coordinatevalues of eye 202A and 202B respectively are determined. An (i)th xcoordinate data represents the location of an (i)th pupil centroid ofthe eye 202A and a (j)th x coordinate data represents the location of an(j)th pupil centroid of the eye 202B. In certain embodiments, steps 550and 555 are performed by controller 1500 using processor 1510, andmicrocode 1522, and instructions 1524. In certain embodiments,controller 1500 wirelessly receives an instruction to perform step 550and 555.

Referring to FIG. 10, in steps of 570 and 575 the method graphicallydisplays a first graph comprising left eye x coordinates versus time.The method further graphically displays a second graph comprising righteye x coordinates versus time. In certain embodiments, steps 570 and 575are performed by controller 1500 using processor 1510, and microcode1522, and instructions 1524. In certain embodiments, controller 1500wirelessly receives an instruction to perform steps 570 and 575.

In step 570, the method for each time value, subtracts a left eye xcoordinate from a right eye x coordinate to form a IPD for that timevalue. In certain embodiments, step 570 is performed by controller 1500using processor 1510, and microcode 1522, and instructions 1524. Incertain embodiments, controller 1500 wirelessly receives an instructionto perform step 570.

FIG. 10 illustrates a first graph showing right eye determined centroidsversus time. FIG. 10 illustrates a second graph showing left eyedetermined centroids versus time. FIG. 10 further illustrates a thirdgraph which comprises for each time value, the difference between a lefteye x coordinate for that time value from a right eye x coordinate forthat time value.

In step 590 and referring to FIG. 10, the dynamic IPDs calculated instep 570 are graphically displayed versus time. In the illustratedembodiment of FIG. 14, three curves of dynamic IPDs versus time fromdifferent sets of video frames of eye movement recorded during differentprocess of visual stimuli′ divergence and convergence match each othersubstantially, which demonstrates a strong reproducibility of theApplicant's method in screening for Convergence Insufficiency.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention.

Referring now to FIGS. 17-18, a desirable product requirement of a CIscreener is the ability to make measurements on a subject withprescription eyeglasses or contact lenses. As shown in FIG. 2A, usingone IR light emitting diode (LED) per eye, this method works wellwithout glasses or with contact lenses, providing a distinctive glintreflection that is easy to detect using established machine visionmethods. However, this does not work well while wearing prescriptionglasses because the prescription lenses also reflect the infrared light,creating an additional glint blocking and obscuring the camera view ofthe glint/pupil/eye.

A standard way to suppress the glasses' reflection is to use a diffuselighting illumination configuration. This is typically done with a ringstructure of LEDs. However, this may be expensive, requiring multipleLEDs in a complex mechanical ring mount. Even more importantly, it mayraise eye safety concerns with so many LEDs in close proximity to theeye.

FIG. 17 shows a unique diffuse illumination method composed of aflexible side glow optical fiber that has a superb light transmissionfor bright and consistent illumination using one or two LEDs. Whenmounted in an eye mask in a ring or oval configuration as shown in FIG.18, it creates a diffuse eye illumination method that suppresses glintreflections from the eyeglasses as well as the eye. Of course, thesefeatures could be added to any of the above embodiments.

Explicit Near Point Convergence Test Disclosure

Referring now to FIG. 19, the standard clinical methods to screen for CIinclude a near point convergence test. This test requires a subject toadjust his focus as well as his convergence while a visual stimulus ismoved in toward his nose. In this way, the subject's ability tosimultaneously accommodate and converge is dynamically tested.

FIG. 2B shows a mechanical configuration which allows the system toexplicitly mimic the clinical near point test. Technically, it is asingle visual stimulus display configuration with a variable imagedistance, all under computer control. FIG. 19 shows an exampleembodiment prototype.

Other features relating to screening devices are disclosed in co-pendingapplication: titled “DEVICE FOR SCREENING CONVERGENCE INSUFFICIENCY ANDRELATED METHODS,” Attorney Docket No. 0127321, which is incorporatedherein by reference in its entirety.

Many modifications and other embodiments of the present disclosure willcome to the mind of one skilled in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. Therefore, it is understood that the present disclosure is notto be limited to the specific embodiments disclosed, and thatmodifications and embodiments are intended to be included within thescope of the appended claims.

That which is claimed is:
 1. A device for screening a person forconvergence insufficiency (CI) with a binocular viewer comprising afirst eyepiece to receive a first eye of the person, a second eyepieceto receive a second eye of the person, a first image sensor adjacent thefirst eyepiece, and a second image sensor adjacent the second eyepiece,the device comprising: a display adjacent the binocular viewer; and aprocessor and associated memory cooperating with said display andconfigured to record, with the first image sensor, movement of the firsteye, record, with the second image sensor, movement of the second eye,display on said display a first visual stimulus and a second visualstimulus, cause, in alternating fashion, convergent movement anddivergent movement in the first visual stimulus and the second visualstimulus along a visual stimulus path, determine respective centroidpositions of the second eye and the first eye during the convergent anddivergent movement of the first visual stimulus and the second visualstimulus, and calculate an interpupillary distance (IPD), and comparethe IPD with the visual stimulus path to obtain a dynamic IPD, thedynamic IPD serving as an indicator for whether the person has CI. 2.The device of claim 1 wherein a duration of each of the convergentmovement and the divergent movement is 80-100 seconds.
 3. The device ofclaim 1 further comprising a first infrared (IR) source configured toirradiate the first eye and a second IR illuminator configured toirradiate second eye; and wherein said processor and memory areconfigured to generate a first plurality of video frames showingmovement of the first eye, and generate a second plurality of videoframes showing movement of the second eye.
 4. The device of claim 3wherein said processor and memory are configured to: identify secondblink pixels comprising second eye blinks in the second plurality ofvideo frames; form a third plurality of video frames by removing thesecond blink pixels from the second plurality of video frames; identifyfirst blink pixels comprising first eye blinks in the first plurality ofvideo frames; and form a fourth plurality of video frames by removingthe first blink pixels from the first plurality of video frames.
 5. Thedevice of claim 3 wherein said processor and memory are configured togenerate the first plurality of video frames by performing at least:filtering each of the first plurality of video frames using a pixelintensity threshold to form a third plurality of video frames, each ofthe third plurality of video frames comprising a black background incombination with a white background, a first eye image, the thirdplurality of video frames comprising an N number of video frames;filtering each of the second plurality of video frames using the pixelintensity threshold to form a fourth plurality of video frames, each ofthe fourth plurality of video frames comprising a black background incombination with a white background, a second eye image, the fourthplurality of video frames comprising an M number of video frames;determining, for each of the third plurality of video frames, x and ycoordinates for a first eye pupil centroid; and generating a firstplurality of x coordinate datasets; wherein an ith x coordinate datasetrepresents a location of an ith second pupil centroid; wherein i isgreater than or equal to 1 and less than or equal to N; determining, foreach of the fourth plurality of video frames, x and y coordinates for asecond eye pupil centroid; and generating a second plurality of xcoordinate datasets; wherein a jth x coordinate dataset represents alocation of a jth first pupilar centroid; wherein j is greater than orequal to 1 and less than or equal to M.
 6. The device of claim 5 whereinsaid processor and memory are configured to: graphically display a firstcurve comprising N x coordinate datasets versus time; and graphicallydisplay a second curve comprising M x coordinate datasets versus time.7. The device of claim 6 wherein said processor and memory areconfigured to: set i=1 and j=1; subtract the ith x coordinate datasetfrom the jth x coordinate dataset to form a kth x coordinate dataset,each of the kth x coordinate dataset represents a hth dynamic IPD; wheni is less than N, set i=i+1; when j is less than M, set j=j+1; andrepeat the setting and the subtracting until at least one of i=N and j=Mis true.
 8. The device of claim 7 wherein said processor and memory areconfigured to form a third curve comprising each of the hth dynamic IPDversus time.
 9. The device of claim 8 wherein said processor and memoryare configured to: identify a first substantially linear portion of thethird curve, the first substantially linear portion comprising apositive slope; identify a second substantially linear portion of thethird curve, the second substantially linear portion comprising anegative slope; generate a graphical plot of the visual stimulus path,the graphical plot comprising a first linear portion comprising apositive slope and a second linear portion comprising a negative slope;overlap the third curve onto the graphical plot of the visual stimuluspath; and adjust the third curve to fit onto graphical plot of thevisual stimulus path.
 10. The device of claim 1 wherein said processorand memory are configured to compare the dynamic IPD with the visualstimulus path by performing at least: optimizing a graph of dynamic IPDswith at least one parameter; and merging the optimized graph of dynamicIPDs with the visual stimulus path.
 11. A non-transitorycomputer-readable medium having computer-executable instructions forcausing a computing device comprising a processor and associated memoryto perform a method for screening a person for convergence insufficiency(CI), the method comprising: recording, with a first image sensor,movement of a first eye of the person; recording, with a second imagesensor, movement of a second eye of the person; displaying on a displaya first visual stimulus and a second visual stimulus; causing, inalternating fashion, convergent movement and divergent movement in thefirst visual stimulus and the second visual stimulus along a visualstimulus path; determining respective centroid positions of the secondeye and the first eye during the convergent and divergent movement ofthe first visual stimulus and the second visual stimulus; andcalculating an interpupillary distance (IPD), and comparing the IPD withthe visual stimulus path to obtain a dynamic IPD, the dynamic IPDserving as an indicator for whether the person has CI.
 12. Thenon-transitory computer-readable medium of claim 11 wherein a durationof each of the convergent movement and the divergent movement is 80-100seconds.
 13. The non-transitory computer-readable medium of claim 11wherein the method comprises: using a first infrared (IR) sourceconfigured to irradiate the first eye and a second IR illuminatorconfigured to irradiate second eye; and generating a first plurality ofvideo frames showing movement of the first eye, and generating a secondplurality of video frames showing movement of the second eye.
 14. Thenon-transitory computer-readable medium of claim 13 wherein the methodcomprises: identifying second blink pixels comprising second eye blinksin the second plurality of video frames; forming a third plurality ofvideo frames by removing the second blink pixels from the secondplurality of video frames; identifying first blink pixels comprisingfirst eye blinks in the first plurality of video frames; and forming afourth plurality of video frames by removing the first blink pixels fromthe first plurality of video frames.
 15. The non-transitorycomputer-readable medium of claim 13 wherein the generating of the firstplurality of video frames comprises: filtering each of the firstplurality of video frames using a pixel intensity threshold to form athird plurality of video frames, each of the third plurality of videoframes comprising a black background in combination with a whitebackground, a first eye image, the third plurality of video framescomprising an N number of video frames; filtering each of the secondplurality of video frames using the pixel intensity threshold to form afourth plurality of video frames, each of the fourth plurality of videoframes comprising a black background in combination with a whitebackground, a second eye image, the fourth plurality of video framescomprising an M number of video frames; determining, for each of thethird plurality of video frames, x and y coordinates for a first eyepupil centroid; and generating a first plurality of x coordinatedatasets; wherein an ith x coordinate dataset represents a location ofan ith second pupil centroid; wherein i is greater than or equal to 1and less than or equal to N; determining, for each of the fourthplurality of video frames, x and y coordinates for a second eye pupilcentroid; and generating a second plurality of x coordinate datasets;wherein a jth x coordinate dataset represents a location of a jth firstpupilar centroid; wherein j is greater than or equal to 1 and less thanor equal to M.
 16. The non-transitory computer-readable medium of claim15 wherein the method comprises: graphically displaying a first curvecomprising N x coordinate datasets versus time; and graphicallydisplaying a second curve comprising M x coordinate datasets versustime.
 17. The non-transitory computer-readable medium of claim 16wherein the method comprises: setting i=1 and j=1; subtracting the ith xcoordinate dataset from the jth x coordinate dataset to form a kth xcoordinate dataset, each of the kth x coordinate dataset represents ahth dynamic IPD; when i is less than N, setting i=i+1; when j is lessthan M, setting j=j+1; and repeating the setting and the subtractinguntil at least one of i=N and j=M is true.
 18. The non-transitorycomputer-readable medium of claim 17 wherein the method comprisesforming a third curve comprising each of the hth dynamic IPD versustime.
 19. The non-transitory computer-readable medium of claim 18wherein the method comprises: identifying a first substantially linearportion of the third curve, the first substantially linear portioncomprising a positive slope; identifying a second substantially linearportion of the third curve, the second substantially linear portioncomprising a negative slope; generating a graphical plot of the visualstimulus path, the graphical plot comprising a first linear portioncomprising a positive slope and a second linear portion comprising anegative slope; overlapping the third curve onto the graphical plot ofthe visual stimulus path; and adjusting the third curve to fit ontographical plot of the visual stimulus path.
 20. The non-transitorycomputer-readable medium of claim 11 wherein the comparing of thedynamic IPD with the visual stimulus path comprises: optimizing a graphof dynamic IPDs with at least one parameter; and merging the optimizedgraph of dynamic IPDs with the visual stimulus path.